Regulators in Oklahoma issued an earthquake advisory and launched an investigation focused on oil and gas wastewater disposal wells after a series of earthquakes struck the state, including a 4.2-magnitude temblor that struck near Edmond, a suburb of Oklahoma City, on Wednesday night.
In a statement Thursday, the Oklahoma Corporation Commission (OCC) said its Induced Seismicity Department was working with the Oklahoma Geological Survey (OGC) to investigate earthquake activity near Edmond. The OCC said the probe was focused on disposal wells that inject into the Arbuckle formation.
"The earthquakes have been clustered close together in an area where there is a known fault," the OCC said. "There are no Arbuckle disposal wells at or very close to the location. There have been no changes to the restrictions placed last year on Arbuckle disposal wells in the Edmond area."
The OCC added that a field inspector from its Oil and Gas Conservation Division (OGCD) has checked eight Arbuckle wells within a 10-mile radius of the earthquake activity, and that recent data on the disposal wells' operations were being reviewed by the commission.
According to the U.S. Geological Survey (USGS), there have been 20 earthquakes measuring at least 2.5-magnitude in the last week. The strongest was Wednesday's 4.2 near Edmond, which struck at 10:56 pm CDT. Since then an additional six earthquakes, ranging from 2.9 to 3.5 in magnitude, have hit the state -- two of them (of 3.3 and 3.5 magnitude) were near Edmond.
News media reports indicated that there was no significant damage from the quakes. The USGS said the epicenter of Wednesday's quake was 6 kilometers (3.7 miles) east-northeast of Edmond.
The OCC and OGCD have been attempting to mitigate induced seismic activity across the state for the last two years. They have focused on wastewater injection wells targeting the Arbuckle -- especially the Mississippian Lime and the Hunton Dewatering play -- within a 15,000-square mile area of interest (AOI) in the state. The OCC said Edmond is located within the AOI.
Scientists with the Oklahoma Geological Survey attribute many of the recent quakes to the disposal of extremely salty water, a byproduct of oil and gas production, via underground injection wells.